Controlled devices are known, which are controlled by a control signal received from a controller (external equipment). Japanese Laid-Open Patent Publication No. H11-338687 (Patent Document 1) discloses a controlled device (expansion unit) as one of such controlled devices, which has an external terminal, a bus interface connected to the external terminal, a memory for storing data, and a processor for receiving a control signal via the external terminal and controlling the memory based on the received control signal. The bus interface is connected to both of the memory and the processor.
This controlled device switches between a first connection state in which the memory and the external terminal are connected via the processor and a second connection state in which the memory and the external terminal are directly connected without involving the processor. Thus, the controlled device is allowed to transmit data between the controller and the memory without involving the processor by switching over the connection state to the second connection state.